1. Field of the Invention
This invention relates to a handset which is used as a part of a telephone, such as one installed in an automobile.
2. Description of the Prior Art
A handset is in common use as a telephone receiver. It is taken off the main body of the telephone to start a telephone call, and is hung up to end it. The use of the handset is detected by a mechanical switching system.
A known handset is disclosed in, for example, the Japanese Patent Application filed by Matsushita Electric Industrial Co., Ltd. on Dec. 20, 1985 and laid open to the public under No. 146052/1987 on Jun. 30, 1987 prior to examination on the merits. It is constructed as shown in FIG. 1 of the accompanying drawings, and is removably held on the main body of a telephone by the combination of mechanical engagement and magnetic attraction. The main body 1 of the telephone has a projection 2 and the handset 7 has a hole 3 in which the projection 2 is removably engaged. The main body 1 is provided with a permanent magnet 4 facing the handset 7. The handset 7 is provided with a magnetic flux detector 5 and a magnetic material 6 both facing the permanent magnet 4. The detector 5 is actuated by detecting the magnetic flux of the permanent magnet 4 and the permanent magnet 4 and the magnetic material 6 produce a magnetic attracting force therebetween.
If the handset 7 is taken off the main body 1, the magnetic flux detector 5 ceases to detect any magnetic flux and produces an OFF signal. If the handset 7 is hung up, the detector 5 detects the magnetic flux of the permanent magnet 4 and produces an ON signal. The magnetic attracting force occurring between the permanent magnet 4 and the magnetic material 6, as well as the engagement of the projection 2 in the hole 3, ensures that the handset 7 be securely held on the main body 1 when hung up.
A switching mechanism including a magnetic catch is disclosed in the Japanese Utility Model Application filed by Uniden Co., Ltd. on Mar. 27, 1987 and laid open to the public under No. 152335/1988 on Oct. 6, 1988 prior to examination on the merits. This mechanism is employed in an automobile telephone set as shown in FIGS. 2 and 3.
The telephone set comprises a base unit 40 and a handset 50. The base unit 40 is provided with a permanent magnet 11 and two yokes 12, and the handset 50 is provided with a principal magnetic member 15 facing the yokes 12. The magnet 11, yokes 12, and magnetic member 15 define a magnetic catch 10 when the magnetic member 15 is attracted by the magnet 11. Each yoke 12 has an edge projection 14 provided for holding the magnetic member 15 by magnetic attraction when the handset 50 is hung up. The edge projection 14 defines an edge portion 13 which is recessed, or located apart from the magnetic member 15 when the handset 50 is hung up. The magnetic member 15 is partly cut so as not to cover fully the adjacent edges of the yokes 12, so that the recessed edge portions 13 of the yokes 12 may allow for the leakage of magnetic flux. The handset 50 is further provided with an auxiliary magnetic member 20 and a magnetic sensor element 30 which face the recessed edge portions 13 of the yokes 12. When the handset 50 is hung up, the leaking magnetic flux flows along a closed path F defined by the recessed edge portions 13 of the yokes 12, the auxiliary magnetic member 20 and the magnetic sensor element 30, and the element 30 outputs an ON signal, while it outputs an OFF signal when the handset 50 is not hung up.
In the device as shown in FIG. 1, however, the same permanent magnet 4 is used for both detecting the handset 7 and holding it and the magnetic detector 5 and the magnetic material 6 are both juxtaposed to the magnet 4. These features make it essential that the magnet 4 be large enough, and that the device as a whole be correspondingly large.
In the device as shown in FIGS. 2 and 3, it is necessary to use a sufficiently long permanent magnet 11 or arrange the relevant parts in a mutually displaced way in order to ensure the leakage of magnetic flux from the magnet 11, while the auxiliary magnetic member 20 is essential for preventing the scattering of the leaking magnetic flux. Therefore, the device necessarily is large and comprises a large number of parts forming a complicated arrangement.
A small size, as well as a high level of performance, is now required of a handset. Moreover, the user is inclined from a standpoint of human engineering to choose a device having a shape defined by many curved lines and planes. While a handset and the main body of a telephone, or a stand on which the handset is placed become smaller, they are, on the contrary, required to contain a greater number of parts to achieve a higher level of performance.
Therefore, a more compact and simpler construction is required of those portions at which the handset is held on the main body of the telephone when hung up. This requirement is also essential to enable the realization of a configuration defined by many curved planes. Moreover, the use of a greater number of parts imposes more restrictions on the possible arrangement of those parts in the limited space defined by the handset or the main body of the telephone and thereby on the possible shape of the handset or the main body of the telephone.
The device as shown in FIG. 1 cannot, however, be constructed with a satisfactorily curved configuration, as it calls for a permanent magnet having a large flat surface area. The device as shown in FIGS. 2 and 3 has already a greatly limited inner space due to the presence of the auxiliary magnetic member and other parts associated therewith.